The hair comprises three layers, namely the outer guard and gloss layer, which is the scaly or flakelike cuticle; a fibrous layer of spindle cells located below it, which is the actual hair shaft or so-called cortex; and finally--in the center of the hair--the core layer, or so-called medulla. This core layer is the moisture carrier for the hair. The moisture penetrates the hair from the scalp inward. If no further moisture is transferred, the hair becomes drier. The hair then behaves differently then.
A newly formed, never-cut hair strand is closed at its end and is thus protected against a loss of moisture. After cutting--over the approximately seven-year life of a single hair strand--however, there is continuously an open end that allows moisture to be lost. This can cause drying and splitting, especially with long hair.
For a rather long time, it has been known to preserve the natural moisture content in hair whose ends have been opened by cutting by sealing it again (cauterizing it) afterward. This has been done for instance using a lighted candle or a gas flame. However, this causes ugly scorched tips at the end of the hair and generally also causes thermal damage to the hair shaft. The attempt has already been made to cut hair using an electric glow wire (French Patent Disclosure FR 26 12 381). However, this greatly limits the flexibility in how to design the hair cut. Moreover, it is very inconvenient. The attempt has also been made to create directly heated scissors and knives (see published French Patent Applications FR 25 32 878 A1 and FR 24 07 797 A1; U.S. Pat. No. 3,892,028; and International Patent WO 92/00688). However, connecting the scissors to the supply lines and embodying the heating devices in the scissors themselves is extremely complicated, and the devices are difficult to manipulate and expensive to design. This cauterizing of the hair has therefore not yet been commercially used.